a. Field of the Invention
This invention relates to a novel process for the preparation of 4'-hydroxybiphenyl-4-carboxylic acid from cyclohexanone-4-carboxylic acid compounds.
b. Description of the Prior Art
4'-Hydroxybiphenyl-4-carboxylic acid is very important as a raw material for the synthesis of polymers and as an intermediate for the synthesis of liquid crystals. Only a few processes for the preparation of this compound have been proposed, and the following three processes are found in the literature.
(a) A process which comprises converting p-phenylphenol into p-methoxybiphenyl, synthesizing 4-methoxy4'-acetobiphenyl therefrom by the Friedel-Crafts reaction, oxidizing it to 4-methoxy-4'-carboxybiphenyl, and then treating the latter with hydrobromic acid to obtain the desired compound [Journal of American Chemical Society, 58, 1738 (1936)]. PA0 (b) A process which comprises reacting p-iodobenzoic acid methyl ester with p-iodoanisole to form 4methoxy-4'-carboxybiphenyl, and then treating it in the same manner as described in the process (a) to obtain the desired compound [Bulletin of the Chemical Society of Japan, 30, 508-13 (1957)]. PA0 (c) A process which comprises diazotizing 4'-aminobiphenyl-4-carboxylic acid and hydrolyzing the resulting product to obtain the desired compound [French Patent No. 735,846].
As to the preparation of cyclohexanone-4-carboxylic acid and its esters which are used, in the process of the present invention, as starting materials for the synthesis of precursors of 4'-hydroxybiphenyl4-carboxylic acid, an attempt has been made to prepare cyclohexanone-4-carboxylic acid methyl or ethyl ester by the hydrogenation of methyl or ethyl 4-hydroxybenzoate (see U.S. Pat. No. 4,537,704).
However, all of the prior art processes for the preparation of 4'-hydroxybiphenyl-4-carboxylic acid require expensive raw materials. Even in the process (a) using relatively cheap p-phenylphenol as the starting material, many steps are required and the raw materials used in each step are expensive. Moreover, this process also involves many problems from the viewpoint of waste disposal. Accordingly, the resulting 4'-hydroxybiphenyl-4-carboxylic acid necessarily becomes quite expensive. Thus, it may safely be said that no industrial process for the preparation of 4'-hydroxybiphenyl-4-carboxylic acid has not been proposed as yet.